77 Sevens: And, two stars meet again

There is a world where magic is widely spread. The story takes place at Tenryou International School, which is famous for an elite training school. The students are divided into three groups, Intelligence, Power and Fate. A school festival is held once a year. The main event is a battle in which a girl and two supporters are chosen from each group and they fight for a selected man, who has a special ring. Yes, the main character is the one who accidentally gets the ring.... While he is persistently chased by heroines, a mystery of their school gradually comes out...